Neutron irradiation can cause the creep rate of a material to increase, decrease, or to remain unchanged. Each of these possible results has been observed in creep during neutron irradiation. In hep alloys increased creep rates have been observed both in Zircaloy-2 and Zr-2.5Nb at creep rates below 10-10 sec-1 at 300 C. At temperatures above 350 C in-reactor creep rates of Zr-2.5Nb are no different from those of unirradiated control tests, whereas in Zircaloy-2 the creep rate may increase, decrease, or remain the same on reactor shutdown, depending on the stress and temperature. Stress relaxation tests reported for zirconium alloys below 100 C resulted in more relaxation during neutron irradiation, suggesting faster creep rates.